The invention relates to a method and a device for mechanically removing solder beads on the surface of printed circuit boards, and to a cold-gas mixer for providing a stream of cold gas for the mechanical removal of solder beads on the surface of printed circuit boards.
When printed circuit boards are flow soldered, so-called solder beads are produced owing to various physical effects. These solder beads can lead to serious functional faults in electronic equipment. In the past, such solder beads were removed by means of a washing process using hydrofluorocarbons (HFCs). Owing to the fact that, for environmental reasons, the use of HFC.s is no longer possible without massive restrictions, methods are used which are not harmful to the environment.
Attempts are therefore being made to prevent the formation of solder beads from the outset by using modified solder resists with repellant properties. Because the solder resist must at the same time adhere to the printed circuit boards, however, the adhesion of solder cannot be completely prevented in this way.
Therefore, in DE-A 44 16 788 it has already been proposed to prevent the adhesion of solder beads on the surface of printed circuit boards by means of an additional artificial cooling with a stream of gas. The intention here is to generate a thermomechanical mismatch between the solder mask and the solder by means of a stream of gas which is at most at room temperature, so that solder beads cannot adhere at all.
In addition to these measures for avoiding the adhesion of solder beads on the surface of printed circuit boards, brush devices are known which can be used to remove the solder beads mechanically. However, it is not possible with this measure to rule out damage to surface mounted devices on the surface of the printed circuit board and to components with connecting wires, or to the printed circuit board in its entirety.